[Qemu-devel] [PATCHv2 2/9] cutils: add a function to find non-zero content in a buffer

[Peter Lieven]

Signed-off-by: Peter Lieven <address@hidden>
---
 include/qemu-common.h |    2 ++
 util/cutils.c         |   40 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 42 insertions(+)

diff --git a/include/qemu-common.h b/include/qemu-common.h
index b59328f..51a7677 100644
--- a/include/qemu-common.h
+++ b/include/qemu-common.h
@@ -362,6 +362,8 @@ size_t qemu_iovec_from_buf(QEMUIOVector *qiov, size_t 
offset,
 size_t qemu_iovec_memset(QEMUIOVector *qiov, size_t offset,
                          int fillc, size_t bytes);
 
+#define BUFFER_FIND_NONZERO_OFFSET_UNROLL_FACTOR 8
+size_t buffer_find_nonzero_offset(const void *buf, size_t len);
 bool buffer_is_zero(const void *buf, size_t len);
 
 void qemu_progress_init(int enabled, float min_skip);
diff --git a/util/cutils.c b/util/cutils.c
index 1439da4..857dd7d 100644
--- a/util/cutils.c
+++ b/util/cutils.c
@@ -143,6 +143,46 @@ int qemu_fdatasync(int fd)
 }
 
 /*
+ * Searches for an area with non-zero content in a buffer
+ *
+ * Attention! The len must be a multiple of 8 * sizeof(VECTYPE) 
+ * and addr must be a multiple of sizeof(VECTYPE) due to 
+ * restriction of optimizations in this function.
+ * 
+ * The return value is the offset of the non-zero area rounded
+ * down to 8 * sizeof(VECTYPE). If the buffer is all zero 
+ * the return value is equal to len.
+ */
+
+size_t buffer_find_nonzero_offset(const void *buf, size_t len)
+{
+    VECTYPE *p = (VECTYPE *)buf;
+    VECTYPE zero = ZERO_SPLAT;
+    size_t i;
+    
+    assert(len % (BUFFER_FIND_NONZERO_OFFSET_UNROLL_FACTOR 
+        * sizeof(VECTYPE)) == 0);
+    assert(((uintptr_t) buf) % sizeof(VECTYPE) == 0);
+
+    if (*((const long *) buf)) {
+        return 0;
+    }
+
+    for (i = 0; i < len / sizeof(VECTYPE); i += 8) {
+               VECTYPE tmp0 = p[i+0] | p[i+1];
+               VECTYPE tmp1 = p[i+2] | p[i+3];
+               VECTYPE tmp2 = p[i+4] | p[i+5];
+               VECTYPE tmp3 = p[i+6] | p[i+7];
+               VECTYPE tmp01 = tmp0 | tmp1;
+               VECTYPE tmp23 = tmp2 | tmp3;
+               if (!ALL_EQ(tmp01 | tmp23, zero)) {
+                   break;
+               }
+    }
+    return i * sizeof(VECTYPE);
+}
+
+/*
  * Checks if a buffer is all zeroes
  *
  * Attention! The len must be a multiple of 4 * sizeof(long) due to
-- 
1.7.9.5